1. Field of the Invention
The present invention is directed to an integrated optical coupler that may be used with an optical multiplexer/demultiplexer or an optical add/drop multiplexer. More particularly, the present invention is directed to such a coupler having at least two optical elements formed on the same surface. When the discrimination feature for performing the coupling is wavelength, the coupler may include a dispersive element.
2. Description of Related Art
Wavelength division multiplexing allows a plurality of different wavelengths to be transmitted over a common transmission line, typically an optical fiber. There are numerous configurations for combining a plurality of different wavelengths from respective sources, i.e., multiplexing, and for selectively directing a combined signal to separate channels, i.e., demultiplexing. When combining wavelength(s) with an already multiplexed signal or removing a wavelength(s) from an already multiplexed signal, this particular type of multiplexing or demultiplexing is typically referred to as adding or dropping, respectively.
Various devices are used to achieve the desired wavelength selectivity. Such devices include dispersive devices, e.g., prisms and diffractive grating devices, and/or fixed or tunable optical filters. Narrow band pass filters demand precise control of the angle of the incident light relative to the filter. Narrow band pass filters can allow a range of wavelengths to pass through different portions thereof by continuously varying the film thickness across the filter aperture. In this configuration, the light beam is incident at the same angle, but due to the varying thickness of the filter, the wavelength selectivity varies. Alternatively, such control of wavelength selectivity may be realized by providing a non-parallel optical block. However, these configurations rely on the precise control of either the thickness or the wedge to insure selectivity.
Integration has been recognized as the way to achieve compact WDM couplers. Currently, such integration typically involves using fibers inserted to either end of a sleeve with a gradient index (GRIN) lens and a filter therein. The angle at which the light is incident on the filter may be adjusted by offsetting the fiber perpendicular to the longitudinal axis of the GRIN lens. However, GRIN lenses are bulky and expensive, limiting the compactness and cheapness that may be achieved even for integrated WDMs.
Further, multiplexing in the time domain is also known. Here, the wavelengths of the signals may be the same, but the time domain is divided so that the signals are interleaved in accordance with a determined time slot corresponding to that signal. These configurations also typically employ GRIN rods. Further, such coupling typically involves bulky polarizing combiners, limiting the integration of the coupler.
The present invention is therefore directed to an integrated coupler that substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
It is an object of the present invention to use the angle versus wavelength variation present in a diffractive optical element to realize wavelength selectivity in conjunction with a wavelength filter. This allows the cost of the system to be lowered by reducing the requirements on the filters. By combining elements which output light at different wavelengths at differing angles with a dielectric filter, the control of the wavelength multiplexing in accordance with the present invention may be realized by optically rather than structurally.
It is a further object of the present invention to provide a compact integrated multiplexer/demultiplexer, particularly one that can be mass-produced by combining at least some of the elements at a wafer level.
It is another object of the present invention to direct light between a beam discriminating element and ports using at least two optical element formed on a single surface.
At least one of the above and other objects may be realized by providing an optical device including a beam discriminating element, which treats signals having at least one different characteristic differently, a first port positioned relative to the beam discriminating element for propagating at least a first signal, a second port positioned relative to the beam discriminating element for propagating at least a second signal, the first and second signals having at least the at least one different characteristic from one another at the beam discriminating element, a third port positioned relative to the beam discriminating element for propagating at least the first signal and the second signal; and a plurality of optical elements, each optical element associated with one of the first through third ports, between an associated port and the beam discriminating element, at least two of the plurality of optical elements formed on a single surface, such that signals are directed between respective ports and the beam discriminating element.
The beam discriminating element may be wavelength sensitive. The beam discriminating element may be polarization sensitive. The beam discriminating element may be a dielectric stack. The optical device may include a polarization rotating element between one of the first and second ports and the beam discriminating element. The beam discriminating element may a multiplexer, the first and second ports serve as input ports, and the third port serves as an output port. The beam discriminating element may be a demultiplexer, the third port serves as an input port, and the first and second ports serves as output ports. The optical elements may dispersive optical elements, e.g., diffractive optical elements. The optical elements may be off-center refractive optical elements.
At least one of the above and other objects of the present invention may be realized by providing an optical device including a wavelength selective filter, a first port positioned relative to the wavelength selective filter for propagating at least a first wavelength, a second port positioned relative to the wavelength selective filter for propagating at least a second wavelength different from the first wavelength signal, a third port positioned relative to the wavelength selective filter for propagating at least the first wavelength and the second wavelength, and at least two dispersive optical elements, each dispersive optical element associated with one of the ports, between an associated port and the wavelength selective filter. The wavelength selective filter and the plurality of dispersive optical elements may be integrated on a substrate level.
At least one of the above and other objects of the present invention may be realized by providing all of the plurality of optical elements may be on a same substrate or on substrates bonded together. The bonding of the substrates results in formation of multiple optical devices, and the bonded substrates are diced to form the optical device. Spacer elements may be provided between the substrates, the spacer elements being bonded to the substrates. The beam discriminating element may be bonded to at least one of the substrates before the substrates are diced. At least some of the plurality of optical elements may be formed on at least two substrates bonded together creating multiple sets of the plurality of optical elements, the bonded substrates being diced to form multiple optical devices.
At least one of the above and other objects may be realized by providing an optical multiplexer including a beam discriminating element, which treats signals having at least one different characteristic differently, a first input port positioned relative to the beam discriminating element for propagating at least a first signal, a second input port positioned relative to the beam discriminating element for propagating at least a second signal, said first and second signals having at least said at least one different characteristic from one another at the beam discriminating element, an output port positioned relative to the beam discriminating element for propagating the first signal and the second signal, and a first substrate that is optically transparent and having first and second opposing faces, wherein all optical elements needed to insure the first and second signals have said at least one characteristic different from one another at the beam discriminating element, and to direct at least one of the first and second signals from the first and second input ports to the beam discriminating element and from the beam discriminating element to the output port, are on at least one of the first substrate and any structure in an optical path in the device bonded to the first substrate.
The first substrate may have at least two of the plurality of optical elements formed thereon. The first substrate may have at least two of the plurality of optical elements formed on a single surface thereof. The plurality of optical elements may include an individual optical element for each port. The bonding of the first substrate and any structure results in formation of multiple optical multiplexers, and the bonded substrates are diced to form the optical multiplexer.
These and other objects of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.